1. Field of the Invention
The present invention relates to a steam turbine blade made of Ti-base alloy, a method of manufacturing the same, a steam turbine power generating plant using the same and a low pressure steam turbine.
2. Description of the Related Art
Conventionally, in a low pressure final stage of a steam turbine, there have been developed 12Cr steel for a blade having 33.5 inch length, Ti-6Al-4V for a blade having 40 inch length, and high strength 12Cr steel for a blade having 43 inch length which is the longest in the world as a machine corresponding to 50 Hz, however, a demand for improving an efficiency and compactifying the plant in accordance that the final blade stage is made long is increased more and more, so that it is required to further lengthen the blade. In order to achieve the requirement, a titanium alloy having a light weight and a high strength is indispensable in place of Ti-6Al-4V which has been practically used.
A titanium alloy in class of tensile strength 95 kg/mm2 can sufficiently correspond to an increase of a centrifugal force caused by the blade having the increased length till the blade having 40 inch, however, in the blade having a length equal to or more than 45 inch, a titanium alloy in class of tensile strength 110 kg/mm2 is required. As the titanium alloy having a tensile strength equal to or more than 110 kg/mm2, there is a xcex2 type titanium alloy having an age hardening property, however, since the xcex2 type titanium alloy has a disadvantage, that is, a toughness is low, there is a problem in manufacturing a whole of the blade by this alloy. On the contrary, in an xcex1+xcex2 type titanium alloy having a high toughness, a cooling speed for a solid solution treatment largely affects the strength in accordance that a dovetail of the blade becomes thick, so that the strength which can be obtained in a small steel lump can not be frequently realized in a large-sized product. Accordingly, it has been hard to securely obtain a titanium alloy in class of 110 kg/mm2.
Further, in Japanese Patent Unexamined Publication No. 1-202389, there is described that a solid solution treatment is executed at a temperature equal to or less than 10 to 60xc2x0 C. corresponding to a point of xcex2 transformation with respect to a condition for a heat treatment of Ti-6Al-6V-2Sn corresponding to an xcex1+xcex2 type high strength Ti alloy, that is, at 867 to 917xc2x0 C. and an age treatment is thereafter executed at 500 to 650xc2x0 C., however, in accordance with this treatment, there has been a problem that the strength can be obtained in a thin blade profile portion, but the strength can not be secured in a thick dovetail portion in which a cooling speed is low.
Further, in Japanese Patent Unexamined Publication No. 7-150316, there is described a turbine blade made of Ti-base alloy containing 3 to 5% of Al, 2.1 to 3.7% of V, 0.85 to 3.15% of Mo and 0.85 to 3.15% of Fe as a material for the turbine blade, however, there is not indicated an age treatment.
An object of the present invention is to provide a steam turbine blade made of Ti-base alloy comprising an xcex1+xcex2 type phase in which a difference of a tensile strength is small between a blade portion and a dovetail portion, a tensile strength at a room temperature of the dovetail portion is equal to or more than 100 kg/mm2 and a suitable toughness is commonly provided together with a strength, as a steam turbine blade having a length of 43 inch or more, a method of manufacturing the same, a steam turbine power generating plant and a low pressure steam turbine.
In accordance with the present invention, there is provided a steam turbine blade having a blade portion and a plurality of fork type or inverted Christmas tree type dovetails, wherein the blade is made of Ti-base alloy structured such that a length of the blade portion is equal to or more than 52 inches with respect to a rotational speed 3000 rpm of the blade or equal to or more than 43 inches with respect to the rotational speed 3600 rpm, and a tensile strength at a room temperature of the dovetail is equal to or more than 100 kg/mm2, preferably equal to or more than 110 kg/mm2 and equal to or more than 96% of the tensile strength at the room temperature of the blade portion.
In accordance with the present invention, there is provided a steam turbine blade, wherein the steam turbine blade is made of Ti-base alloy containing Al 4 to 8 weight %, V 4 to 8 weight % and Sn 1 to 4 weight %, a tensile strength of the dovetail at a room temperature is equal to or more than 100 kg/mm2, preferably equal to or more than 110 kg/mm2, a V notch impact value (y) at a room temperature is equal to or more than a value (kgxe2x88x92m) calculated by a formula (xe2x88x920.0213x+4.025), or the blade portion is structured such that a tensile strength (x) thereof at a room temperature is equal to or more than 105 kg/mm2, the V notch impact value (y) at a room temperature is equal to or more than a value (kgxe2x88x92m) calculated by a formula (xe2x88x920.0196x+3.93) and the tensile strength of the dovetail at a room temperature is equal to or more than 96% of the tensile strength of the blade portion at a room temperature.
In accordance with the present invention, there is provided a steam turbine blade, where in the blade is made of Ti-base alloy structured such that a length of the blade portion is equal to or more than 52 inches with respect to a rotational speed 3000 rpm of the blade or equal to or more than 43 inches with respect to the rotational speed 3600 rpm and Al 4 to 8 weight %, V 4 to 8 weight % and Sn 1 to 4 weight % are contained, the blade portion is structured such that a tensile strength (x) at room temperature is equal to or more than 105 kg/mm2 and V notch impact value (y) at a room temperature is equal to or more than a value (kg-m) calculated by a formula (xe2x88x920.0196x+3.93), or the dovetail is structured such that a tensile strength (x) at a room temperature is equal to or more than 100 kg/mm2 and a V notch impact value (y) at a room temperature is equal to or more than a value (kgxe2x88x92m) calculated by a formula (xe2x88x920.0213x+4.025).
In accordance with the present invention, there is provided a method of manufacturing a steam turbine blade made of Ti-base alloy, wherein a solid solution treatment and an age treatment is performed so as to cool by water after heating in a range connecting four points shown by reference symbols A (605xc2x0 C. and 855xc2x0 C.), B (590xc2x0 C. and 790xc2x0 C.), C (410xc2x0 C. and 790xc2x0 C.) and D (410xc2x0 C. and 855xc2x0 C.) expressed by (an age temperature and a solid solution treatment temperature) shown in FIG. 1 of this application, wherein the area expressed by (the age temperature and the solid solution treatment temperature) is structured such that a solid solution treatment and an age treatment is performed so as to cool by water after heating in a range connecting four points shown by reference symbols E (525xc2x0 C. and 855xc2x0 C.,), F (510xc2x0 C. and 790xc2x0 C.), G (410xc2x0 C. and 790xc2x0 C.) and H (410xc2x0 C. and 855xc2x0 C.) shown in FIG. 2 of this application, wherein the dovetail portion is roughly processed to a state close to a final shape prior to a final heat treatment and next a solid solution treatment and an age treatment is performed so as to cool by water after heating in a range connecting four points shown by reference symbols J (685xc2x0 C. and 855xc2x0 C.), K (585xc2x0 C. and 790xc2x0 C.), L (410xc2x0 C. and 790xc2x0 C.) and M (410xc2x0 C. and 855xc2x0 C.) expressed by (an age temperature and a solid solution treatment temperature) shown in FIG. 3 of this application, and wherein the dovetail portion is roughly processed to a state close to a final shape prior to a final heat treatment and next a solid solution treatment and an age treatment is performed so as to cool by water after heating in a range connecting four points shown by reference symbols N (575xc2x0 C. and 855xc2x0 C.), O (560xc2x0 C. and 790xc2x0 C.), P (410xc2x0 C. and 790xc2x0 C.) and Q (410xc2x0 C. and 855xc2x0 C.) expressed by (an age temperature and a solid solution treatment temperature) shown in FIG. 4 of this application.
In accordance with the present invention, there is provided a steam turbine power generating plant comprising a high pressure turbine, an intermediate pressure turbine and a low pressure turbine, wherein a rotor blade at a final stage of the low pressure turbine has a blade portion and a plurality of fork-like dovetails and is constituted by the steam turbine blade mentioned above.
In accordance with the present invention, there is provided a low pressure steam turbine comprising a rotor shaft, a rotor blade provided on the rotor shaft, a stator blade guiding an inlet of a steam to the rotor blade and an internal casing holding the stator blade, wherein the rotor blade is structured in a dual current such that six stages of the rotor blades are provided in each of right and left portions of the steam turbine in a symmetrical manner and a first stage is provided in a center portion of the rotor shaft, and a rotor blade at the final stage is constituted by the steam turbine blade mentioned above.
The Ti-base alloy is heated to a temperature area having an xcex1+xcex2 phase and held at the temperature area after a hot forging and thereafter is forcibly cooled (solid solution treated), whereby an xcex1 phase and xcex1xe2x80x2 martensite two phase structure is refined and homogenized, so that a high ductility and a high toughness can be obtained. Further, due to the successive aging treatment, the xcex1xe2x80x2 martensite is decomposed to the xcex1+xcex2 two phase so as to form a duplex state comprising a pro-eutectoid xcex1 grain and an old xcex2 grain from which the xcex1 phase is precipitated due to the aging (aging hardening), whereby a high tensile strength and a high fatigue strength can be obtained.
The temperature for the solid solution treatment is properly selected in a range between 800 and 900xc2x0 C. corresponding to a temperature equal to or less than a xcex2 transformation point (about 927xc2x0 C.) particularly in the case of Ti-6%Al-6%V-2%Sn among the Ti-base alloy containing 4 to 8% of Al, 4 to 8% of V and 1 to 4% of Sn. In particular, the temperature of 790 to 855xc2x0 C. is more preferable by combination. At the temperature equal to or more than the xcex2 transformation point, a reduction of the ductility and the toughness is caused due to a roughness of a crystal grain and a reduction of an amount of the pro-eutectoid xcex1 grain. Further, when the temperature for the solid solution treatment is set too low, the amount of the pro-eutectoid xcex1 grain is increased as well as the hot forging structure is left, so that a proper strength can not be obtained.
The subsequent temperature for the aging treatment is properly selected in a range between 500 and 600xc2x0 C. The higher the temperature for the aging treatment is, the more the tensile strength is reduced, so that the ductility and the toughness are improved. In particular, a special combination at the temperature between 410 and 685xc2x0 C. is preferable by a combination with the temperature for the solid solution treatment.
The reasons of the preferable range for the components of the Ti-base alloy used in the present invention are as follows.
Al: This is a representative xcex1 stabilizing element and is an indispensable additional element for the (xcex1+xcex2) type Ti-base alloy. It is hard to become the (xcex1+xcex2) type alloy when an amount of Al is less than 4%, and it is hard to obtain a sufficient strength for a material. On the contrary, when an amount of Al is over 10%, Ti3Al corresponding to an intermetallic compound is generated and a toughness is significantly reduced, so that it is not preferable. In particular, an amount of Al is preferably set to 4 to 8%.
V: This is an important additional element for reducing the xcex2 transformation point as well as stabilizing the xcex2 phase. This has an effect of restricting a rapid generation and increase of the xcex1 phase after an annealing or the solid solution treatment so as to finely precipitate the xcex1 phase. In the case that a contained amount of V is less than 4%, it is not possible to sufficiently reduce the xcex2 transformation point and the effect of stabilizing the xcex2 phase is reduced, so that it is impossible to obtain the effect of restricting the generation of the xcex1 phase during the annealing or after the solid solution treatment. On the contrary, when a contained amount of V is over 10%, the stability of the xcex2 phase becomes too large and it is hard to obtain a preferable two phase (xcex1+xcex2) structure, so that it is insufficient in view of a strength. In particular, the contained amount of V is preferably set to 4 to 8%.
Sn: This has an effect of stabilizing the xcex2 phase and simultaneously restricting a grain growth. Accordingly, as well as Al, in addition that this is important for restricting a rapid generation and increased of the xcex1 phase after the annealing or after the solid solution treatment so as to finely precipitate the xcex1 phase, this has an effect of refining the whole of the structure, so that this is an additional component occupying an important position for strengthening. When the contained mount of Sn is less than 1%, a crystal grain is enlarged during the annealing or after the solid solution treatment and it is hard to obtain the desired effect mentioned above. On the contrary, when the contained amount of Sn is over 5%, the xcex2 phase is stabilized too much and it is hard to obtain the preferable two phase structure, so that an improvement of a higher strength can not be desired. In particular, the contained amount of Sn is preferably set to 1 to 4%.
The Ti-base alloy mentioned above is employed for the final stage rotor blade in the low pressure turbine at a blade length of 43 inches or more with respect to 3600 rpm and 52 inches or more with respect to 3000 rpm, in particular, an alloy comprising 5 to 7% of Al, 5 to 7% of V, 1 to 3% of Sn, 0.2 to 1.5% of Fe, 0.20% or less of O, 0.3 to 1.5% of Cu and the remainder of Ti, and it is preferable to apply the same heat treatment as mentioned above.
The conditions mentioned above can be applied to the following inventions.
In accordance with the present invention, there is provided a steam turbine power generating plant mentioned above, wherein the high pressure turbine and the intermediate pressure turbine or the high and intermediate pressure turbine are structured such that a temperature of an inlet for a steam to the first stage rotor blade is in a range of 538 to 660xc2x0 C. (preferably, 593 to 620xc2x0 C., 620 to 630xc2x0 C. and 630 to 640xc2x0 C.), the low pressure turbine is structured such that a temperature of an inlet for a steam to the first stage rotor blade is in a range of 350 to 400xc2x0 C., and a rotor shaft exposed to the steam inlet temperature of the high pressure turbine and the intermediate pressure turbine or the high and intermediate pressure turbine or a whole of the rotor shaft, a rotor blade, a stator blade and an internal casing is constituted by a high strength martensite steel containing 8 to 13 weight % of Cr, or the first stage, or the second stage or the third stage of the rotor blade among them is constituted by a Ni-base alloy.
It is preferable that the high pressure turbine, the intermediate pressure turbine or the high and intermediate pressure turbine in accordance with the present invention has a rotor blade provided in the rotor shaft, a stator blade guiding an inlet of a steam to the rotor blade and an internal casing holding the stator blade, a temperature of the steam flowing into the first stage of the rotor blade is 538 to 660xc2x0 C. and a pressure thereof is 250 kgf/cm2 or more (preferably, 246 to 316 kgf/cm2) or 170 to 200 kgf/cm2, the rotor shaft or the rotor shaft, the rotor blade and at least first stage of the stator blade is constituted by a high strength martensite steel having a whole tempered martensite structure containing 8.5 to 13 weight % (preferably, 10.5 to 11.5 weight %) of Cr corresponding to 10 kgf/mm2 of 105 time creep breaking strength or more (preferably, 17 kgf/mm2 or more) at a temperature in correspondence to each of the steam temperatures (preferably, 566xc2x0 C., 593xc2x0 C., 610xc2x0 C., 625xc2x0 C., 640xc2x0 C., 650xc2x0 C. and 660xc2x0 C.), or the first stage or the second stage or the third stage of the rotor lade among them is constituted by the Ni-base alloy, and the internal casing is constituted by a martensite casting steel containing 8 to 9.5 weight % of Cr having 10 kgf/mm2 of 105 time creep breaking strength or more (preferably, 10.5 kgf/mm2 or more) at a temperature in correspondence to each of the steam temperatures, thereby heating the steam flowing out from the high pressure steam turbine, the intermediate pressure steam turbine or the high pressure side turbine so as to heat to a level equal to or more the high pressure side inlet temperature and feed to the intermediate pressure side turbine, whereby the high and intermediate pressure integral type steam turbine can be obtained.
In the high pressure turbine and the intermediate pressure turbine or the high and intermediate pressure integral type steam turbine, the rotor shaft of the first stage of at least one of the rotor blade and the stator blade is preferably constituted by a high strength martensite steel containing in weight 0.05 to 0.20% of C, 0.6% or less, preferably 0.15% of Si, 1.5% or less, preferably 0.05 to 1.5% of Mn, 8.5 to 13%, preferably 9.5 to 13% of Cr, 0.05 to 1.0% of Ni, 0.05 to 0.5%, preferably 0.05 to 0.35% of V, 0.01 to 0.20% of at least one of Nb and Ta, 0.01 to 0.1%, preferably 0.01 to 0.06% of N, 1.5% or less, preferably 0.05 to 1.5% of Mo, 0.1 to 4.0%, preferably 1.0 to 4.0% of W, 10% or less, preferably 0.5 to 10% of Co, 0.03% or less, preferably 0.0005 to 0.03% of B and 78% or more of Fe, and it is preferable to correspond to the steam temperature of 593 to 660xc2x0 C., or it is preferable to be constituted by a high strength martensite steel containing 0.1 to 0.25% of C, 0.6% or less of Si, 1.5% or less of Mn, 8.5 to 13% of Cr, 0.05 to 1.0% of Ni, 0.05 to 0.5% of V, 0.10 to 0.65% of W, 0.01 to 0.20% of at least one of Nb and Ta, 0.1% or less of Al, 1.5% or less of Mo, 0.025 to 0.1% of N and 80% or more of Fe, and it is preferable to correspond to a temperature less than 600 to 620xc2x0 C. Said internal casing is preferably constituted by a high strength martensite steel containing in weight 0.06 to 0.16% of C, 0.5% or less of Si, 1% or less of Mn, 0.2 to 1.0% of Ni, 8 to 12% of Cr, 0.05 to 0.35% of V, 0.01 to 0.15% of at least one of Nb and Ta, 0.01 to 0.8% of N, 1% or less of Mo, 1 to 4% of W, 0.0005 to 0.003% of B and 85% or more of Fe.
In the steam turbine power generating plant in accordance with the present invention, the high pressure steam turbine is structured such that the rotor blade is provided at seven stages or more, preferably, at nine to twelve stages, and the first stage is constructed in a dual current, the intermediate pressure steam turbine is structured such that the rotor blade is provided at six or more stages in a symmetrical manner in each of the right and left lines, and the first stage is provided in a center portion of the rotor shaft so as to form a dual current construction, the high and intermediate pressure integral type steam turbine is structured such that the high pressure side rotor blade is provided at six stages or more, preferably seven stages or more and more preferably eight stages or more and the intermediate pressure side rotor blade is provided at five stages or more, preferably six stages or more, and the low pressure steam turbine is structured such that the rotor blade is provided at five stages or more, preferably six stages or more and more preferably eight to ten stages in a symmetrical manner in each of the right and left lines and the first stage is provided in a center portion of the rotor shaft so as to form a dual current construction.
The low pressure turbine in accordance with the present invention is structured such that the steam inlet temperature to the first stage rotor blade is preferably set to 350 to 400xc2x0 C., and the rotor shaft thereof is preferably constituted by Ni-Cr-Mo-V low alloy steel which is structured such that a distance (L) between centers of bearings is 6500 mm or more (preferably, 6600 to 7500 mm), a minimum diameter (D) at a portion in which the stator blade is provided is 750 to 1300 mm (preferably, 760 to 900 mm), and a value (L/D) is 5 to 10, preferably 7 to 10 (more preferably, 8.0 to 9.0) and 3.25 to 4.25 weight % of Ni is contained.
The low pressure steam turbine in accordance with the present invention is preferably structured by any one of the following items or a combination thereof. A length of the blade portion is 80 to 1300 mm from an upstream side of the steam current to a downstream side, a diameter of the mounting portion of the rotor blade in the rotor shaft is greater than a diameter of the portion corresponding to the stator blade, a width in an axial direction of the mounting portion in the downstream side is increased preferably at three or more stages (more preferably, four to seven stages) step by step in comparison with the upstream side and a rate with respect to the length of the blade portion is 0.2 to 0.8 (preferably, 0.3 to 0.55) and is made smaller from the upstream side to the downstream side. Said length of the blade portion in each of the adjacent stages is made greater in the downstream side in comparison with the upstream side, and the ratio thereof is in a range of 1.2 to 1.8 (preferably, 1.4 to 1.6) and the ratio is gradually made greater in the downstream side. The width in an axial direction of the portion corresponding to the stator blade portion in the rotor shaft is made preferably three stages or more (more preferably, four to seven stages) greater in the downstream side in comparison with the upstream side, a rate with respect to the length of the downstream side blade portion in the rotor blade is in a range of 0.2 to 1.4 (preferably, 0.25 to 1.25, in particular, 0.5 to 0.9) and the rate is made smaller to the downstream side step by step.
Hereinafter, the other constituting material of the low pressure turbine will be described below.
(1) The low pressure steam turbine rotor shaft is preferably constituted by a low alloy steel having a fully temper bainite structure containing in weight 0.2 to 0.35% of C, 0.1% or less of Si, 0.2% or less of Mn, 3.25 to 4.25% of Cr, 0.1 to 0.6% of Mo, and 0.05 to 0.25% of V, and is preferably manufactured in accordance with the same manufacturing method as that of the high pressure and intermediate pressure rotor shaft mentioned above. In particular, it is preferable to manufacture in a super cleaning manner which uses a raw material having an impurity such as P, S, As, Sb, Sn and the like which is made as low as possible in addition to 0.01 to 0.5% of Si and 0.05 to 0.2% of Mn, whereby a total amount of the impurity in the employed raw material is reduced to a level of 0.025 or less. 0.010% or less of P and S, 0.005% or less of Sn and As and 0.001% of Sb are preferable.
(2) The other stages than the final stage of the low pressure turbine plate and the nozzle are preferably constituted by a fully temper martensite steel containing 0.05 to 0.2% of C, 0.1 to 0.5% of Si, 0.2 to 1.0% of Mn, 10 to 13% of Cr, 0.04 to 0.2% of Mo.
(3) The internal and external casings for the low pressure turbine are both constituted by a carbon casting steel containing 0.2 to 0.3% of C, 0.3 to 0.7% of Si and 1% or less of Mn.
(4) A main steam stopper valve casing and a steam adjusting valve casing are constituted by a fully temper martensite steel containing 0.1 to 0.2% of C, 0.1 to 0.4% of Si, 0.2 to 1.0% of Mn, 8.5 to 10.5% of Cr, 0.3 to 1.0% of Mo, 1.0 to 3.0% of W, 0.1 to 0.3% of V, 0.03 to 0.1% of Nb, 0.03 to 0.08% of N and 0.0005 to 0.003% of B.